It seems that after about two days of riding my rear brakes are soft. I rebleed them, two rides later, soft again. This went on for most of last season. Also, everytime I bleed them the fluid is foggy black. I don't think I 'm burning the fluid because I ride my wife's bike, same trails and 07 codes with no problem. And I also use DOT 5.1 fluid. Any suggestions would be appreciated.